Final answer:
The nurse should withhold the varicella vaccine if the client is allergic to neomycin.
Step-by-step explanation:
When administering the varicella vaccine to a young adult female client who has not previously had chickenpox or its vaccine, the nurse should withhold the vaccine and collect additional data when the client makes the statement, "I am allergic to neomycin." This is because the varicella vaccine contains neomycin, an antibiotic, as a preservative. It is important to avoid administering the vaccine to individuals who are allergic to neomycin to prevent an allergic reaction.